Plant-microbe-mediated decrease of greenhouse gases under dynamic wetland hydrology

Abstract

<jats:title>Abstract</jats:title><jats:p>While wetlands represent a small fraction (~7%) of the world’s land surface, it is estimated that one third of wetlands have been lost due to human activities. Wetland habitat loss decreases ecosystem functions such as improving water quality and mitigating climate change. These microbially mediated functions are dependent on particular soil redox conditions, which are altered by soil hydrology and the presence of plants. Differences in microbial physiology allow certain taxa (aerobes and facultative anaerobes) to adapt to fluctuating (dry/wet) hydrologic conditions, while other taxa (obligate anaerobes) are better adapted to continually saturated conditions. Therefore, the duration of hydrologic periods can affect soil microbial community structure and function. Further, plant-derived carbon, nutrients, and air are released by diffusion belowground which also impacts microbial activity in soils. In this study, we hypothesized that redox status due to continuous flooding would support greater abundance of microbial taxa involved in methanogenesis (obligate anaerobes), but plant-mediated oxygen transport would decrease methane emissions. Using a mesocosm design, we manipulated duration of hydrologic condition (i.e., stable dry, stable flooding, and alternating wet/dry) and presence of plants to induce soil redox changes in wetland soils. We measured soil redox status, used targeted amplicon sequencing to characterize the bacterial and archaeal communities, and measured greenhouse gas production to assess microbial function. Hydrology and to a lesser degree plant presence influenced soil redox conditions. Hydrologic history strongly influenced microbial community composition, but plant presence and hydrologic treatment altered microbial function to a great degree. As predicted, plant presence decreased greenhouse gas production in the wetland mesocosms. While previous studies do not often include plants when assessing greenhouse gas emissions, this study highlights that plant-mediated decreases in greenhouse gas emissions are significant. If plant-mediated effects are not considered when estimating the carbon balance of ecosystems, then wetland carbon storage could be underestimated.</jats:p>

Metagenomes from Experimental Hydrologic Manipulation of Restored Coastal Plain Wetland Soils (Tyrell County, North Carolina)

“…Here, we present wetland soil metagenomes from a mesocosm experiment in which we manipulated hydrology and plant presence to examine microbial community responses. These data complement targeted amplicon sequencing data, GHG fluxes, and soil physicochemical properties from the wetland mesocosm experiment ( 9 ).…”

“…We altered redox conditions by manipulating hydrology over 8 weeks. The experimental design and sampling details were published by Bledsoe and Peralta ( 9 ). We collected and combined six soil cores (3-cm diameter, 10-cm depth) from plant or no-plant areas.…”

“…We collected and combined six soil cores (3-cm diameter, 10-cm depth) from plant or no-plant areas. We completed 16S rRNA amplicon sequencing (NCBI BioProject PRJNA636184 ), GHG flux measurements, and soil environmental analyses ( 9 ). We sequenced metagenomes that represented the most distinct microbial communities based on amplicon sequencing, and we chose the following samples: wetland soils sampled from field sites at which the water table measured −20 cm and 0 cm, to capture “mesocosm baseline” ( n = 8) functional diversity, and a subset of samples at the end of the 8-week hydrologic manipulation (i.e., prolonged drying or wetting only) in the presence or absence of vegetation ( n = 16) ( 9 ).…”

Hydrological Conditions Influence Soil and Methane-Cycling Microbial Populations in Seasonally Saturated Wetlands

“…Previously published literature suggests that relatively short-term changes in hydrology (i.e., hours to 6 mo.) impact soil function (Foulquier et al, 2013), but the underlying structure of the microbial composition is shaped by former and long-term historical trends in hydrology (Banerjee et al, 2016;Bledsoe and Peralta, 2020;Veach and Zeglin, 2020). That being said, small but sustained changes in hydrology could surpass thresholds and lead to fundamental changes in the structure and function of the microbial community (Lee et al, 2018).…”

“…Such dynamic hydroperiods influence every aspect of these systems -from the ecology and breeding success of amphibian species (Chandler et al, 2017) to soil nutrient cycling (Marton et al, 2015;Hansen et al, 2018). These variable hydrologic conditions also stimulate the aerobic and anaerobic heterotrophic decomposition of organic C, resulting in the production and emission of two important greenhouse gases: carbon dioxide (CO 2 ) and methane (CH 4 ) (Bansal et al, 2016;Kifner et al, 2018;Bledsoe and Peralta, 2020). The extent to which wetlands produce and emit greenhouse gases is intimately tied to the underlying soil microbial population; however, insights into seasonal wetland microbial communities are poorly understood.…”